Understanding and Applying Energy Density in Your Diet

The term energy density refers to the amount of kilocalories provided by a certain volume of a product. It is most commonly expressed in units of kcal/g or kcal/100 g, although it can also be found as kcal/ml (for beverages and other liquids). The range of values for this parameter lies between 0 and 9 kcal/g. Four main categories of products can be distinguished based on their energy density: products with very low energy density: < 0.6 kcal/g, products with low energy density: 0.6-1.5 kcal/g, products with medium energy density: 1.6-3.9 kcal/g, and products with high energy density: > 4 kcal/g.

The energy density of a product is established by its components. Fat, as the component with the highest energy value, has the greatest impact on increasing energy density. Conversely, a high proportion of water in the product significantly decreases it. Carbohydrates and proteins cause a moderate increase in the energy density of the product, while the presence of fiber reduces it, but to a lesser extent than water.

The lowest energy density is found in water (0 kcal/g) and other non-energetic or low-energy liquids (coffee and tea without additives, zero beverages). Most fruits and vegetables with low starch content, as well as broth-based soups (e.g. raisins, minced beans and some creams) have very low values. This is due to the high water content in these products. The low energy density group includes low fat (yogurt, yogurt, milk, etc.), lean meat and vegetable seeds, liquid plant seeds, and dense plant seeds and meat. It is important to note that the energy density of the product after heat treatment decreases due to the higher water content. For example, dry bulgur provides 3.4 kcal in 1 g, after cooking it is 0.8 kcal/g. The medium energy density characterizes m.in. fatty meats and meat products, bread (bread, rolls, some cakes), cheese, fatty fish, and low-fat snacks (e.g. pretzels, biscuits). The group of products with high energy density includes salty and fried snacks (chips, fries, crackers), sweets, fast food, nuts, seeds, and other products with high fat content (e.g. butter, mayonnaise, some sauces). The highest values concern oils, which consist exclusively of fat – 1 g provides about 9 kcal.

It is probably sufficient in daily life to follow general guidelines regarding the energy density values of different product groups. However, if there is any doubt as to which category a food belongs to, you can use the nutritional value table on each product. In this table, you can check the energy content information in 100 g and divide that number by 100 to get the energy density value in 1 g. If a product delivers 284 kcal per 100 g, its energy densities are 2.84 kcal/g and it can be classified as a medium-energy density group. Determining the energy density of meals, such as those prepared at home, requires a bit more attention. In this case, it is necessary to determine the calorie content and size of the entire portion (e.g. using a calorie counting app). If a meal provides 327 kcal per 230 g portion, its energy density will be 1.42 kcal/g, which is considered a low value.

It's crucial to emphasize that energy density differs from nutrient density. The latter refers solely to the amount of energy provided by products, while the former mainly focuses on the quantity of nutrients supplied in a certain volume, which are both beneficial to health (e.g. fiber, iron, calcium, potassium, vitamins A, C, and E) and detrimental (saturated fatty acids, trans fats, simple sugars, sodium). In practice, this means that not all low-energy products will have a high concentration of essential nutrients. At the same time, high-energy products don't necessarily possess a low nutritional value. For example, creamy ice creams provide 1.65 kcal/g, classifying them as products with low to moderate energy density. However, more than 40% of the energy originates from simple sugar, and over 20% from saturated fatty acids. In the case of almonds, which are high-energy products (6.26 kcal/g), they contain fiber, calcium, and iron, and the fat content present in them primarily consists of unsaturated fatty acids.

The application of energy density is contingent on the diet's objective. In a balanced, health-focused diet aimed at maintaining body weight, it is important to consider various product groups. The foundation should consist of those with very low energy, such as vegetables and fruits, which should be supplemented with low- and medium-energy whole grains, vegetable or animal protein sources. In moderation, healthy fats, including plant oils, nuts, and seeds, should also be incorporated. Limiting products high in energy yet low in nutritional value, such as sweets, fast food, or salty snacks, is recommended. When aiming for weight loss, the proportions of different products in the diet should shift towards those with lower energy density. Special attention should be given to high-energy products, as even those with high nutritional value can impede achieving the set goal if consumed in excess. Commencing meals with a low-energy snack (e.g., salads, soups) can assist in weight loss by partially filling the stomach and inducing a feeling of fullness earlier, potentially decreasing calorie intake. Scientific studies corroborate this relationship, with a 2016 review observing a clear association between consuming low-energy products and weight loss in overweight individuals, attributed to the consistency of food intake outweighing calorie intake variation. Consequently, if high-energy products are replaced with lower-energy alternatives while portion size remains unchanged, the body may experience similar satisfaction despite lower calorie intake (M. Stelmach-Mardas et al., 2016). Employing this strategy also facilitated maintaining weight loss outcomes over several months (B. J. Rolls, 2017). Conversely, to increase body weight, high-energy products should be more prevalent in the diet. This way, even small food quantities can provide substantial energy. However, the selection of products is vital - they should also have high nutritional value. To augment a meal's energy density, consider adding plant oils, seeds, or nuts to savory dishes and nut butter or whole-grain flakes to sweet dishes. Besides low-energy fruits and vegetables, opt for those with higher energy density (e.g., bananas, avocados, potatoes, or sweet potatoes). Increasing the frequency of egg and fatty fish consumption is also advantageous.